Many physiological and pathophysiological conditions can be influenced by presenting a cell, cell culture, or organism with a drug that directly or indirectly interferes with that condition. For example, drugs that directly interfere with a physiological and pathophysiological condition include enzyme inhibitors (e.g., penicillin inhibits bacterial transpeptidases, or lovastatin/MK-803 [Mevinolin™] inhibits 3-hydroxy-3-methylglutaryl coenzyme A reductase) or antisense nucleic acids (e.g., antisense DNA inhibit translation of viral genes). Although directly interfering drugs are often highly specific towards their target, their biological action is frequently limited to individual biochemical conversions or processes.
In order to modulate a plurality of biochemical reactions or physiological events, drugs that modulate signal transduction pathways may be employed, and numerous compositions and methods are known in the art to interfere with signal transduction pathways. For example, in one method of interfering with a signal transduction pathway, a signaling molecule (e.g., a cytokine or insulin) is added to a cell or organism. Adding signaling molecules is often advantageous, especially where exogenous addition to a system lacking the signaling molecule reconstitutes the physiologically normal level of the signaling molecule. However, addition of exogenous signaling molecules is frequently problematic, especially where the molecules are immunogenic peptides or peptide preparations with impurities and/or inhomogeneities.
Alternatively, receptors for the signaling molecules may be blocked or otherwise rendered functionally inactive. For example, a beta-blocker competitively inhibits binding of the natural signal adrenalin to beta-adrenergic receptors in the nervous system. Receptor blockers generally exhibit strong inhibition of their target receptors; however, tend to inhibit non-target receptors, especially where the non-target receptors belong to the same family as the target receptor (e.g., various beta-blockers tend to block non-target beta-2 receptors).
In another example, elements within a signaling cascade may be inhibited to prevent a signal from being transduced to the target compartment of a cell. A particularly promising element in a signaling cascade is the vascular endothelial growth factor (VEGF) receptor kinase, which specifically phosphorylates its substrate in dependence of binding of VEGF to the VEGF receptor, and it has recently been shown, that VEGF kinase inhibitors effectively inhibit signaling in VEGF kinase associated pathways [Drevs J. et al. Effects of PTK787/ZK 222584, a specific inhibitor of vascular endothelial growth factor receptor tyrosine kinases, on primary tumor, metastasis, vessel density, and blood flow in a murine renal cell carcinoma model. Cancer Res 2000; 60(17):4819-24]. However, even relatively low cross-reactivity with kinases other than VEGF kinases may potentially disrupt a plethora of non-targeted pathways due to the presence of various kinases in many other signaling pathways.
In a still further example, elements and processes at the end-point of a signaling cascade may be inhibited to prevent the signal from being translated into a regulatory or other function in the cell. A typical example of “end-point inhibition” is the use of antisense nucleic acids that hybridize with a transcription product that is being formed in a response to the signal, or that form triple helices with a target sequence that is activated by the signal.
Although there are various methods of interfering with signal transduction pathways known in the art, all or almost all of them suffer from one or more disadvantages. Therefore, there is a need to provide novel methods for interfering with signal transduction pathways.
Vitamin A-derivatives (retinoids) occur physiologically mostly in the form of retinol, retinaldehyde and retinoic acid. The latter was recognized as the form preventing vitamin deprivation conditions. Known mediators of retinoid effects on gene expression are transcription factors of the class II steroid/thyroid family: the retinoic acid receptors isoforms (RARalpha, RARbeta, RARgamma) which are inducible by all-trans RA, and the mammalian retinoid X receptor isoforms (RXRalpha, RXRbeta, RXRgamma) which are inducible by 9cis-RA. The general toxicity of retinoic acid and retinoids (Biesalski H K; Comparative assessment of the toxicology of vitamin A and retinoids in man, Toxicology 57, 117-161, 1989; Kamm et al. Preclinical and clinical toxicology of selected retinoids, the retinoids 2, p. 287-326, 1984) has been motivation to identify more selective retinoids. Aided by test systems of cells overexpressing distinct isoforms of RAR and/or RXR, it has become feasible to design and test novel retinoid agonists that display considerable receptor selectivity (see for example U.S. Pat. No. 6,096,787; Graupner et al., Biochem. Biophys. Res. Comm. 179(3):1554-1561, 1991; Lehmann et al., Retinoids selective for retinoid X receptor response pathways, Science 258, 1944-1946, 1992). Further development in chemical derivatization generated receptor-selective antagonists for RAR or RXR, and also retinoids that allowed to dissociate receptor-mediated reporter gene activation from receptor-mediated gene repression (e.g. Chen et al., RAR-specific agonists/antagonists which dissociate transactivation and AP-1 transrepression inhibit anchorage-independent cell proliferation, EMBO J 14, 1187-1197, 1995), or receptor-selective agonists that are susceptible to geometric determinants of the promoter context, such as spacing of DNA recognition sites (Benoit G et al, RAR-independent RXR signaling induces t(15;17) leukemia cell maturation, EMBO J 18(24), 7011-7018, 1999). Most importantly, clinical trials with receptor-selective retinoids (Miller V A et al., Initial clinical trial of a selective retinoid X receptor ligand, LGD1069, J. Clin. Oncol. 15, 790-795, 1997) indicated that the toxicity profile of selective retinoids is different from the well-known toxicity profile of retinoic acid in humans as reported by Biesalski et al.; further development of highly receptor-selective compounds with rigid backbone structures did not generate a favorable toxicity profile. Therefore, it is desirable to develop retinoids that display a different repertoire of interactions, characterized by selectivity for non-receptor pathways that would be expected to be more cell-specific expected. Preferably, such retinoids would interfering selectively with signal transduction pathways. It is apparent from the literature that the cumulative toxicity after administration of cis-configured retinoid stereoisomers is different from the cumulative toxicity seen after administration of all-trans-configured retinoids. It is therefore important to appreciate that targets of all-trans retinoids are not the same as targets of cis-configured retinoids. Thus, the identification of a polypeptide target for all-trans-configured retinoids does not specify that the particular polypeptide is also a target of cis-configured retinoids.